The present invention relates to the field of crystalline semiconductor materials and their processes for production, particularly crystals of CdTe, CdZnTe, CdSeTe or CdZnSeTe having a high resistivity, and has for its object a process for the production of such crystals, a corresponding crystalline material as well as various applications of such a material.
In numerous applications, it is necessary to have crystals of CdTe, CdZnTe, CdSeTe or CdZnSeTe having a high resistivity, which is to say typically at least equal to and preferably greater than 109 ohms cm.
It has been known for several decades that cadmium telluride cannot be obtained in a semi-insulating form (resistivity >109 ohms) without chemical composition, and this no matter what the process of growth, because of the presence of lacunae of electrically active cadmium, which must be compensated. This has been demonstrated, both by modeling and by experimental results.
According to the present state of the art, this high resistivity is obtained by doping with a single doping element, introduced in the course of the process of production. We thus speak of a “compensation process”.
Among the doping elements, chlorine, in the form of cadmium chloride, is most generally used, but indium or aluminum are also used.
Among the processes for production, the growth by the so-called methods of “transfer from a solvent zone” (such as those known by the terms “traveling solvent method” or “traveling heater method” or “traveling gradient zone melting”) is historically the most used, but growth by so-called “Bridgman” methods (Bridgman high pressure or BHP, Bridgman low pressure, Bridgman in sealed ampoule etc.) are more and more often advocated, all these methods forming a part of the methods called crystallization in liquid phase.
The methods of growth by crystallization in gaseous phase can also use the same process for compensation by doping with a doping element.
The mentioned processes for production, associated with compensation mechanisms, are well known to those skilled in the art and have for example been described in the following documents: FR-A-2 172 231; FR-A-2 228 540; FR-A-2 314 759; “Deep centers for optical processing in CdTe”, E. Rzepha et al., Materials Science and Engineering, B16(1993), 262-267, Elsevier Sequoia; “Deep levels in smi-insulating CdTe”, P. Moravec et al., Materials Science and Engineering, B16 (1993), 223-227, Elsevier Sequoia.
Similarly, devices for their practice have also been known (see for example FR-A-2 332 799).
However, the electrical quality (particularly the degree of resistivity) of the crystals obtained by these known processes, is extremely subject to the skill and experience of the operators.
In fact, the residual impurities inevitably present in the material, play a substantial role, evidently by interaction with the dopant voluntarily added and/or with the lacunae of cadmium (and/or zinc) systematically present in the crystal.